Ultrasonic atomizer for waste sulfuric acid and use thereof in acid cracking furnaces

ABSTRACT

Ultrasonic atomizer nozzle assembly for atomizing waste sulfuric acid in a cracking furnace in which the acid feed stream is mechanically broken up by a stationary or rotating type atomizer into a coarse spray and an annullarly arranged ultrasonic generator further atomizes the coarse spray into microscopic particles. The ultrasonic generating gas is deflected into the ultrasonic resonance chamber and the coarse spray is either centrally or annularly positioned relative to the ultrasonic field. An annular gas buffer may be provided around the atomizer. The nozzle assembly is mounted in the ceiling of a furnace having a gas flow constricting member spaced from the ceiling 1-4 times the diameter of the furnace.

United States Patent Kerner et al.

[ 1 Sept. 30, 1975 ULTRASONIC ATOMIZER FOR WASTE SULFURIC ACID AND USETHEREOF IN ACID CRACKING FURNACES [75] Inventors: Walter Kerner,Hermulheim;

Friedrich Mahler, C ologne-Nippes; Heinrich Peters, Lowenich, all ofGermany [73] Assignee: Davy Powergas GmbH, Cologne.

Germany [22] Filed: Oct. 12, 1973 [21] Appl. No.: 405,908

[30] Foreign Application Priority Data Oct. 14. 1972 Germany 2250521Nov. 17, 1972 Germany 2256442 [52] US. Cl. 239/4 [51] Int. Cl.'- B05B17/04 [581 Field of Search 239/4, 102; 431/1, 190; 23/277 R, 277 C. 262;423/540 [56] References Cited UNlTED STATES PATENTS 2.481.620 9/1949Rosenthal 239/4 3.243.122 3/1966 Snaper 239/4 3,375,977 4/1968Butterworth et a1. 239/4 3,469,785 9/1969 Boucher et a1, 239/4 3,746,2577/1973 Broad et a1. 239/102 Primary Examiner-Lloyd L. King Attorney,Agent, or Firm-Millen. Raptes & White [57] ABSTRACT cles. The ultrasonicgenerating gas is deflected into the ultrasonic resonance chamber andthe coarse spray is either centrally or annularly positioned relative tothe ultrasonic field. An annular gas buffer may be provided around theatomizer. The nozzle assembly is mounted in the ceiling of a furnacehaving a gas flow constricting member spaced from the ceiling 14 timesthe diameter of the furnace.

10 Claims, 5 Drawing Figures US. Pamnt Sept. 30,1975 Sheet 1 of33,908,904

US. Patsnt Sept. 30,1975 Sheet 2 of3 3,908,904

U.S. Patent Sept. 30,1975 Sheet 3 Of3 3,908,904

6 .1 6 we 6 0 M U P I 7///// vv////////A///7/////// i!" l I I I A I m lu: I I I I r 1 r I 1 l I 1 s q fl \\\\Y\\.l|!- II/ m...) x A///// /A//AA) /A/////////A///////////// d 8 l 6 6 ULTRASONIC ATOMIZER FOR WASTESULFURIC ACID AND USE THEREOF IN ACID CRACKING URNACES BACKGROUND OF THEINVENTION This invention relates to ultrasonic atomizers for theatomization of waste sulfuric acid in cracking furnaces, as well as to afurnace equipped with these ultrasonic atomizers.

In a number of chemical processes, waste sulfuric acids containingvarying amounts of impurities are obtained, which latter can be removedonly by expensive procedures. Therefore, these acids, containing besideswater primarily organic compounds, e.g., sulfonic acids, sulfates, suchas, for example ammonium sulfate or metallic sulfates, or metallicoxides, are split reductively at temperatures of between about 850 andl250C., forming an SO -containing cracked gas which can beconventionally processed according to the contact method to obtainconcentrated sulfuric acid or oleum. The thermal energy required for thecracking step is generated by the combustion of oil or heating gas inthe cracking furnace.

Heretofore, cracking yields of up to 98% have been attained, i.e., 98%of the hexavalent sulfur contained in the waste sulfuricacid is present,after the cracking step, sulfur dioxide, and the remainder is further inthe hexavalent,form as sulfuric acid vapor and/or sulfur trioxide.Besides, the cracked gases are largely laden with ashes produced by thecombustion of the contaminants contained in the waste sulfuric acids.Thus, the hot cracking gases must be cooled and cleaned before they arefed to the sulfuric acid plant. In the cooling of the cracked gasesfrom, for example, about 1000 C. to about 350 C., the waste heat thereofis generally utilized for air heating and/or high-pressure steamgeneration in air preheaters or waste heat boilers. It was found thatthe two percent of unreduced sulfuric acid and in some cases sulfuricacid compounds in the cracked gases, together with the other gasimpurities, can lead to corrosive attacks on the air preheaters or wasteheat boilers. During the subsequent gas scrubbing step, the hexavalentsulfur compounds contained in the cracked gas enter at leastpartiallyinto the scrubbing water and thus are lost for the sulfuricacid recovery. Consequently, there is the need for increasing thecracking yield to an optimum value lying almost at 100%.

In order to introduce the waste sulfuric acid into the cracking furnace,air atomizer nozzles of a large cross section have heretofore beenpreferably employed for the feeding and discharging of the acid, sincemost of the waste sulfuric acids contain considerable impurities in theform of solid substances and/or polymerization products. Because ofthese contaminants,-pure pressure atomizer nozzles tend to clog,resulting in disturbances in the operation. With the heretofore utilizedair atomizer nozzles, it has been necessary to use, for throughputefficiencies of up to 20 tons of acid per hour and more, 0.5 to 0.8 Nmof air under a pressure of 5000 mm. H O column per kg. ofacid,-depending on the constitution of the acid, in order to atomizetheacid. In this process, droplet sizes of between 400 and 600 1. couldbe obtained, with the most frequent droplet size being 500 ,u.. Thedisadvantage which is particu-' larly significant for the furtherprocessing .of the cracked gas to sulfuric acid is, in the airatomization method, the dilution of the cracked gas, resulting inincreased expenditures for extra apparatus in the sulfuric acid portionof the total plant. In contrast thereto, if the excess of air is reducedat the oil burners in order to compensate for this increased consumptionof air, a larger furnace space is required for complete combustion, andthe cracking process, with irregular acid atomization, becomes moresusceptible to breakdown. An improvement of the yield of the crackingprocess by increasing the residence time in the furnace leads perforceto an increase in furnace volume and thus to risfuel combustion in thefurnace.

SUMMARY OF THE INVENTION The ultrasonic atomizer riozzle assembly ofthis invention comprises an ultrasonic generator for generating anultrasonic field, said generator having an operative end faceand'resonanc'e chamber having an outlet opening disposed at said endface, a first conduit for feeding the operating medium to said chamber,and means for producing ultrasonic sound in said operating medium, asecond conduit for feeding a stream of said waste sulfuric acid, anatomizer for converting said stream into a coarse spray positionedadjacent saidoperative end face of said ultrasonic generator, one ofsaid atomizer and said resonance chamber substantially surrounding theother, whereby the ultrasonic sound energy is distributed throughoutsaid coa rse spray.

Waste sulfuric acid either contains'initially solid substances, or isfreed of such substances during the atomizing step. Therefore, pressureand rotary atomizers for waste sulfuric acids tend to clog rapidly andthus are quickly prone to disturbances in operation, if the atomvization is to be conducted so that the fineness required for anextensive cracking step is produced. It has now been found that thesedisturbances are avoided and yet a considerable increase in the crackingyield can be attained by conducting a coarse atomizing by means of thepressure or rotary atomizer into an ultrasonic field.

The nozzle width and/or the ejected film thickness is selected to be solarge that the impurities contained in the acid cannot impair theatomization process. Subsequently, the thus-produced droplet cone and/orfilm is extremely finely atomized in the ultrasonicfield, resulting inan increase in the cracking yield of of up to at least 99.5%. Thereby,the susceptibility to corrosion of the cooling devices connecteddownstream of the cracking furnace is reduced, and the yield ofregenerated sulfuric acid is increased.

DETAILED DISCUSSION tained in the acid, which solids can have a diameterof up to 1 mm. or higher.

In accordance with the preferred embodiment of this invention, thepressure or rotary atomizer is accommodated in a central cavity of theultrasound generator, wherein the nozzle of the pressure atomizer or thecentrifugal edge of the rotary atomizer is arranged in the end surfacearea of the ultrasound generator. Due to the construction of theultrasound generator in the form of a hollow cylinder, in the interiorof which is the pressure or rotary atomizer, an optimum utilization ofthe ultrasonic field is achieved for the fine atomization, and a compactatomizer construction suitable for installation in cracking furnacesresults therefrom.

Suitably, the annular slot between the pressure or rotary atomizer andthe ultrasound generator is in communication with a compressed-gassource via a conduit. The gas feed to the annular slot between theatomizer and the ultrasound generator is merely to avoid the entrance ofthe acidic furnace atmosphere into this annular slot and any possiblecondensation and corrosion on the internal parts of the ultrasonicatomizer. Accordingly, the conduit serves only to maintain a gas bufferin the annular slot. The air feed into the furnace is effected almostexclusively at the burners, rather than through the annular slot betweenthe atomizer and the ultrasound generator. The nebulization is attained,

, without the aid of an atomizing gas, solely by the rapid introductionof the pre-atomized acid into the ultrasonic fieldflhe droplets producedby the preliminary atomization have an average particle size of betweenI 0.2 and 2 mm.

In accordance with the preferred embodiment of this invention, anultrasonic atomizer is utilized operating with low-pressure steam as theoperating medium for the ultrasound generator.

For the generation of the ultrasonic field, lowpressure steam isemployed of 0.6 l atmospheres gauge, preferable 0.6 4 atmospheres gauge.The use of steam as the operating medium for the ultrasound generatorhas the advantage that the steam can be condensed out of the cracked gasand thus does not result in a dilution of the contact gas. Theultrasound generator of the acid atomizer of this invention can also beoperated, in place of steam, with compressed air or a combustible gas.For the operation of the ultrasound generator, only a fraction(maximally 50%) of the amount of air is required which is otherwisenecessary for the atomization of the same quantity of waste acid in anair atomizer nozzle. The operating medium flows at very high speed alongthe deflection element into the annular resonance chamber and is excitedtherein to ultrasonic vibrations. The high-energy sonic waves areconducted to the acid cone to be atomized, and the latter is extremelyfinely divided by the sonic field. The ultrasonic atomizer is usable,besides for the nebulization of waste sulfuric acid, also for theatomization of waste solutions containing salts (ammonium salts) ofsulfur-containing acids.

Preferably, the rotary atomizer consists of a cup axially joined to arotary drive shaft and of a feed pipe for the acid terminating in thecup. The feed pipe has lateral openings, through which the acid exitsradially and is conveyed against the inner surface of the cup, thelatter rotating at a speed of about 4000 7000 r.p.m., depending on thethroughput efficiency. The sheet formed on the internal surface of thecup by the centrifugal effect is torn apart at the cup edge intodroplets which, due to their centrifugal force, enter the sonic field ofthe ultrasound generator. Suitably, the rotary drive shaft isconstructed as a quill shaft, and the feed pipe is extended axiallythrough the quill shaft for rotation therewith, up into the cup. Thisprovides a simple feed of the acid into the cup rotating at a highspeed.

In its most general scope, the invention concerns an ultrasonic atomizerfor the atomization of waste sulfuric acid in cracking furnaces,consisting of an ultrasound generator with an annular resonance chamberdisposed at the end face, a conduit for the feeding of the operatingmedium, and a deflecting element for the guidance of the stream ofoperating medium from the feed conduit into the resonance chamber,wherein the atomizer is characterized in that the mouth of a feed ductfor the waste sulfuric acid to be atomized is arranged in the closeproximity to the.ultrasound generator.

Such ultrasonic atomizers operating with an ultrasound generator(Hartmann generator) are known per se in ultrasonic oil burners.However, heretofore, the general opinion was that the atomizingprinciple utilized in ultrasonic oil burners could not be suitable forthe atomization of waste sulfuric acids, because heating oil is apractically homogeneous liquid, while the contaminated waste sulfuricacids either initially contain solids or precipitate solids during theatomization. Consequently, waste sulfuric acid must be introduced in aconsiderably larger layer thickness into the ultrasonic field thanheating oil, so that it was to be expected that the fine degree ofatomization known from the oil could not be attained in case of wastesulfuric acids. Also, there have been misgivings insofar as theendothermic acid cleavage, with irregular atomization (caused by solidcomponents and fluctuating atomization behavior on account of changes inthe composition and thus in the physical values governing for theatomization process, such as surface tension, viscosity), is much moresusceptible to disturbances "(flame subcooling) than the exothermic oilcombustion.

In accordance with the preferred embodiment of this invention, theultrasound generator is surrounded by the outlet opening of the feedduct for the waste sulfuric acid. The annular exit slot of the feed ducthas preferably a maximum slot width of 1 mm. An atomizing nozzle withsuch an external ring-shaped acid discharge slot is suitable for theatomization of waste sulfuric acids having solid particles of up to asize of 0.5 mm. in diameter.

In accordance with another embodiment of the invention the dischargeopening of the feed duct for the waste sulfuric acid is arrangedcentrally in the ultrasound generator, especially axially within thedeflection element. The feed duct is suitably an axially linear bore,the diameter of which can be up to maximally 10 mm. This embodiment issuitable for strongly contaminated waste sulfuric acids having solidsparticles of up to several millimeters in diameter.

The furnace for the waste acid dissociation is characterized, accordingto the invention, in that a burner for the fuel required for the acidcracking process is centrally arranged in the furnace ceiling, and theultrasonic atomizers are distributed around the burner, and that afurnace body constriction is provided at a spacing from the furnaceceiling amounting to 14 times, especially 1.5 3 times the diameter ofthe furnace. The

brick-lined cracking furnace has generally a cylindrical configurationand is preferably vertically disposed. By

the arrangement, according to this invention, of the burner, the acidatomizers, and the furnace body constriction, an axial current isproduced in the furnace chamber from the furnace ceiling to the furnacebody constriction, and a gaseous flow is formed at the periphery of thefurnace chamber which is directed from the constriction to the furnaceceiling. Thereby, the almost complete cracking of the waste sulfuricacid is achieved in a relatively small furnace volume, resulting in areduction of the height or length of the furnace as compared toheretofore customary cracking furnaces.

Advantageously, the ultrasonic atomizers are distributed around theburner in a uniform concentric arrangement. This provides an axiallysymmetrical gas circulation in the furnace chamber. Furthermore, thefurnace body constriction is suitably equipped with gas passage openingson the furnace wall. Thus, the objective is attained that only thoseportions of the hot combustion gas stream where practically a completecracking has been attained can pass through the passage openings, ratherthan gas still laden with acid mist. The ultrasonic atomizers alsopermit the alteration of the configuration of the acid mist from anelongated up to a short, bulging shape, likewise resulting in a maximumutilization of the cracking furnace volume and an increase in thecracking yield.

Advantageously, the burner for the production of the cracking heat inthe furnace is a pulsed oil burner. The pulsed oil burner is arranged ina burner muffle axially attached to the ceiling of the cracking furnace,so that already the hot combustion gases enter at a high speed (up to150 m./sec.) in parallel to the acid mists into the cracking furnace. Ascompared to the heretofore customary heating of the cracking furnaceswith directly attached burners, there is no longer the danger that aflame subcooling is caused by the endothermic acid cracking process, andaccordingly a disturbance of the cracking step is avoided.

A special advantage of the ultrasonic atomizers of this invention incracking furnaces for waste sulfuric acid resides in that only arelatively minor amount of low-pressure steam as compared to the amountof acid to be atomized is required for the production of the high-energyultrasonic field. The steam consumption ranges between 0.1 and 0.3 kg.of steam per kg. of waste sulfuric acid, depending on the constitutionof the acid. This results in advantages for the cracking process and thesubsequent sulfuric acid production, as can be seen from the followingcomparison of the ultrasonic atomizer of the present invention with theacid atomization by means of air atomizer nozzles.

The requirements and the resultant products are as follows for thecracking of 1 kg. of waste sulfuric acid having the chemical compositionof:

58.00 7? H 50. 32.03 H O (5000 mm. H O column) t 50C.

-Continued 58.00 H 32.03 H O 2.00 organic substance 7.77 NH 0.2annealing residue Air Atomizer Ultrasonic Nozzle Nozzle (2) AtomizingkgJkg. 0.1 0.2

*vapor needed Acid (SS 4 atm. gauge) (3) Fuel quantity kgJkg. L25l.Ol-O.986

for producing Acid needed thermal energy for cracking process (fuel oilwith 9800 kcal-lkg.) (4) Air excess for n 1.03 1.27-1 .274

fuel combustion at burners (combustion air preheating) C 500 500 (5)Cracked gas Nm lkg. 2.72 2.56-2.68

quantity dis Acid charged (moist) cracking furnace (6) Contact gas quan-Nm lkg. 3.09 2.95-2.94

tity at entrance Acid to H 80, plant (based on same 0 /50 ratio 1.32)

saturated steam It can be seen from the comparison that, with the use ofthe steam-operated ultrasonic atomizer of this invention, there is areduction of the fuel consumption in the cracking furnace by 25%, adecrease in the thusproduced cracked gas by 25% and in the amount ofcontact gas by 4.5%. This represents an essential saving in operatingdevices and a reduction in the initial investment costs, since thesize'of the sulfuric acid plant connected thereafter is determinedsubstantially by the amount of the contact gas to be passed therethrough. Steam-operated ultrasonic atomizers make it possible to work thepulsed burner. with an air excess of n 1.27, so that burned-outcombustion gases enter from the muffle of the pulsed burner into thecracking furnace chamber, whereas,in air atomizers and directly attachedburners operated with an air excess of n 1.03, the complete combustionis attained only after the flame extends about 23 :m. into the furnacechamber, whereby, in case of an irregular acid atomization, a flamesubcooling and a disturbance of the cracking process can easily occur.In spite of the thusdemonstrated advantages inherent in-the ultrasonicatomizer, the result is a reduction of the contact gas quantity, asindicated in the table, together with a corresponding increase of thesulfur dioxide concentration in the contact gas.

DESCRIPTION OF THE DRAWINGS The invention will be described in greaterdetail with reference to the drawings as set forth below, in which:

FIG. 1 shows an axial sectional view of a first embodiment of theultrasonic atomizer nozzle of this invention;

FIG. 2 shows an axial sectional view of a second embodiment of theultrasonic atomizer nozzle of this invention;

FIG. 3 shows an axial sectional view of a third embodiment of theultrasonic atomizer nozzle of this invention;

FIG. 4 shows an axial sectional view of a fourth embodiment of theultrasonic atomizer nozzle of this inventiomand FIG. 5"shows an axialsectional view of the cracking furnace of the present invention in aschematic representation.

According to FIG. 1, the atomizer nozzle 1 consists of an annularultrasound generator 3 with a resonance chamber 3, to which theoperating medium is fed via the annular chamber 3", the bores 3 and theannular through the interior 2 of the pipe 2 and through the bores 16"into the turbulence chamber 16. From the turbulence chamber, the acidpasses through the opening 16 and enters the ultrasonic field, emanatingfrom 'the resonance chamber 3, in the form of a cone of coarselyatomized droplets.

The embodiment shown in FIG. 2 differs from the embodiment of FIG. 1essentially in that a rotary atomizer 19 is arranged in the cavity 3" ofthe ultrasound generator 3 in place of the pressure atomizer 16 Therotary atomizer 19 comprises essentially an atomizing cup 19, attachedat one end'of a quill shaft 17 rotat- "-ahiy supported in the bearings18. The hollow shaft 17 isco nne cted to a rotary drive (not shown) in asuitable manner. A feed pipe 20 for the acid is coaxially 'rhoun't'ed inthe quill shaft 17 and extends with its front end into the distributingcup 19. At its front end, the fe'ed pipe 20 has several lateral openings20 for the disi charg ing' of the acid into the cup 19. The annular 'spaceil5 between the rotary atomizer 19 and the ultra sound generator 3can be connected, via a pipeline to a'compressed-gas source (not shown),so that a gas buffercan beformed in the annular space 15, preventing theentrance of cracked gas. During the operation of this atomizer nozzle,the acid fed through pipe and exiting through openings 20 is forcedagainst the inside of the cup 19' rotating at a high speed. The acidspreads like a sheet over the inner wall of the cup and isflung fromthecup edge 19 in the form of droplets into the ultrasonic field,wherein they are converted into a fine mist;

According to FIG. 3, the atomizer nozzle 1 consists of a front sleeve 1with an internal thread and a rear sleeve 3 .with an external thread.The sleeves l and 3 are threadedly connected with the interposition of aspacer ring 1. An annular projection 3" is formed at the sleeve 3,extending forwardly approximately to the front edge of the sleeve 1;this projection flares at the front end and contains a forwardly openresonance chamber 3. An axial sleeve 3" having an internal threadis'mounted to the front sleeve portion 3' and is connected to the latterwith the aid of spokes; the deflecting element 5 with the guide surface5 is threadedly inserted in this axial sleeve. The waste sulfuric acidis fed through the annular duct 2 and the bores 3 of the sleeve 3 to theoutlet opening 2 formed as an annular slot. The operating medium (steam)required for the production of the ultrasonic field is conducted throughthe internal duct 4, between the spokes 3 along the de- .flectionsurface 5 into the annular resonance chamber In accordingto FIG. 4, thereso- I been threadedly inserted into the sleeve 3, the deflectingelement S is threadedly inserted into the inner thread ofthe mountingring 14 to such an extent that the operating medium fed through theannular duct 4 is deflected at the guide surface 5 into the resonancechamber 3f. Furthermore, a sleeve 13 is threadedly inserted into theouter sleeve 3; this sleeve 13 forms, together with the rear end of thedeflecting element 5, the annular duct 4 for feeding the operatingmedium for the generation of ultrasound.'The waste sulfuric acid to beatomized is supplied through the central bore 2 in the deflectionelement 5 and enters the ultrasonic field produced by the resonancechamber 3 at the front aperture 2". r

' FIG. 5 shows a vertical cracking furnace 6, wherein a burner mufflewith a burner 7 is centrally attached at the ceiling 6. thereof; theburner is provided with feed 7 pipes for air and fuel oil (7" and 7",respectively). Furthermore, several ultrasonic atomizers 1] are arrangedin the furnace ceiling in concentric distribution around the burner 7these atomizers are adjustable in the vertical direction with the aid ofa lance 8. A flame bridge 6 is formed in the furnace chamber at aspacing from the furnace ceiling corresponding to 2.5 times the diameterof the furnace chamber. The flame bridge 6 has gas passages 6 beside thefurnace wall 6".

symmetrical gas circulation 11, wherein the vaporization and cracking ofthe acid are conducted. By the conductance of the combustion gases, theobject is achieved that these gases circulate at least partially in thecracking chamber between the ceiling 6 and the 7' bridge 6 before theyflow through the openings 6 to the cracked gas outlet 12.

The ultrasonic nebulization of the acid, in conjunction with thecirculation of the completely burnt-out combustion gases in thecombustion chamber, makes it possible to achieve an almost completereduction of the hexavalent sulfur contained in the atomized solutionsto sulfur dioxide.

What is claimed is:

1. A method of atomizing in a furnace aqueous waste sulfuric acidcontaining suspended solids or dissolved salts which precipitate uponatomization of the acid which comprises the combination of steps offirst mechanically converting a feed stream of the aqueous acid into acoarse spray and further atomizing the coarse spray by passing itthrough a field of ultrasonic sound.

2. A method according .to claim 1 wherein the frequency of theultrasonic field is between 20 and kilohertz.

3. A method according to claim 1 wherein the average particle size ofthe coarse spray is between 0.2 and 2 mm. and the average particle sizeof the further atomized spray is between 1 and 200 u.

4. A'method according toclaim 1 wherein the ultrasonic field is providedby steam at 0.6-10 atmospheres gauge pressure.

5. A method according to claim 1 wherein the frequency of the ultrasonicfield is between 20 and 100 kilohertz and wherein the average particlesize of the coarse spray is between 0.2 and 2 mm. and the averageparticle size of the further atomized spray is between 50 and 80 p.

6. A method of atomizing acid solutions containing sulfur and alsocontaining impurities of suspended solids or dissolved salts whichprecipitate upon atomization of the acid solution comprising developingan ultrasonic field in free space;

converting a feed stream of the acid sulfur solution containing saidimpurities into a coarse spray; and ejecting said coarse spraycontaining said impurities into said electronic field in free space.

7. A method according to claim 6, wherein said impurities have adiameter of up to substantially 0.5 mm and wherein said step ofdeveloping an ultrasonic field includes the step of passing steamthrough a central bore, and wherein said step of converting a feedstream into a coarse spray includes the step of feeding said feed streamthrough an annular space surrounding said central bore and through anannular exit slot having a maximum width of about 1 mm.

8. A method according to claim 6 wherein said impurities have a diameterof up to several millimeters and wherein the step of converting a fieldstream into a coarse spray includes the step of feeding said feed streamthrough a central bore and wherein said step of developing an ultrasonicfield includes the step of passing steam through an annular spacesurrounding said central bore.

9. A method according to claim 8, wherein said central bore has amaximum diameter of about 10 mm.

10. A method according to claim 8, wherein said step of converting afeed stream into a coarse spray also includes the step of forcing saidfeed stream against the inner surface of a cup rotating at a speed ofabout 4000 to 7000 rpm.

1. A method of atomizing in a furnace aqueous waste sulfuric acidcontaining suspended solids or dissolved salts which precipitate uponatomization of the acid which comprises the combination of steps offirst mechanically converting a feed stream of the aqueous acid into acoarse spray and further atomizing the coarse spray by passing itthrough a field of ultrasonic sound.
 2. A method according to claim 1wherein the frequency of the ultrasonic field is between 20 and 100kilohertz.
 3. A method according to claim 1 wherein the average particlesize of the coarse spray is between 0.2 and 2 mm. and the averageparticle size of the further atomized spray is between 1 and 200 Mu . 4.A method according to claim 1 wherein the ultrasonic field is providedby steam at 0.6-10 atmospheres gauge pressure.
 5. A method according toclaim 1 wherein the frequency of the ultrasonic field is between 20 and100 kilohertz and wherein the average particle size of the coarse sprayis between 0.2 and 2 mm. and the average particle size of the furtheratomized spray is between 50 and 80 Mu .
 6. A method of atomizing acidsolutions containing sulfur and also containing impurities of suspendedsolids or dissolved salts which precipitate upon atomization of the acidsolution comprising developing an ultrasonic field in free space;converting a feed stream of the acid sulfur solution containing saidimpurities into a coarse spray; and ejecting said coarse spraycontaining said impurities into said electronic field in free space. 7.A method according to claim 6, wherein said impurities have a diameterof up to substantially 0.5 mm and wherein said step of developing anultrasonic field includes the step of passing steam through a centralbore, and wherein said step of converting a feed stream into a coarsespray includes the step of feeding said feed stream through an annularspace surrounding said central bore and through an annular exit slothaving a maximum width of about 1 mm.
 8. A method according to claim 6wherein said impurities have a diameter of up to several millimeters andwherein the step of converting a field stream into a coarse sprayincludes the step of feeding said feed stream through a central bore andwherein said step of developing an ultrasonic field includes the step ofpassing steam through an annular space surrounding said central bore. 9.A method according to claim 8, wherein said central bore has a maximumdiameter of about 10 mm.
 10. A method according to claim 8, wherein saidstep of converting a feed stream into a coarse spray also includes thestep of forcing said feed stream against the inner surface of a cuprotating at a speed of about 4000 to 7000 r.p.m.